Type of problem: Due to the increased load, the original concrete beam has insufficient bearing capacity, and the reinforcement method needs to be reinforced with carbon fiber cloth

Parameters of the tensioned carbon fiber sheet at the bottom of the beam:  

Carbon fiber cloth grade: Grade I

Elastic modulus Ecf= 2.30×10^⁵MPa 

Design value of tensile strength ff= 2300.00 MPa 

Single layer thickness tcfv= 0.167 mm 

Weight: 300g/m2  does not consider the secondary force

Calculation results

1. After the load of the KL3 beam is increased, the area of the missing reinforcement is 750mm², and the carbon fiber cloth paste size is converted by the principle of equal strength substitution:

Design value of tensile strength of HRB400 steel bar: 360N/mm²

Design value of tensile strength of carbon fiber cloth: 2300N/mm² 

Lack of reinforcement area * design value of tensile strength of steel bar ≤ design value of carbon fiber cloth thickness * width * design value of tensile strength of carbon fiber cloth  

750*360≤0.167*width*2300  

Width≥702.94  

The KL3 beam section size is 400*900, and the structural beam width of 400 cannot meet the carbon fiber cloth bonding width. Consider bonding double-layer carbon fiber cloth, and calculate the carbon fiber cloth multi-layer bonding reduction factor:  

Reduction factor=1.16-(paste layer number*elastic modulus design value*single layer degree)/308000≤0.9=1.16-(2*230000*0.167)/308000=0.91  

Reduction factor=0.9  

750*360≤0.167*width*2300*0.9 

Width ≥781.05  

The width of KL3 beam is 400mm, and the double-layer area of carbon fiber cloth paste: 2*400=800≥781.05, which meets the strength requirements.